Map集合遍历的五种方式

1.通过Map.KeySet遍历key和value

for (String key : map.keySet()) {
            String value = map.get(key);
            System.out.println("key: " + key + " value: " + value);
        }

2.通过Map.entrySet使用iterator遍历key和value

Iterator.Entry> iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = iterator.next();
            System.out.println("key: " + entry.getKey() + " value: " + entry.getValue());
        }

3.通过Map.entrySet遍历key和value

for (Map.Entry entry : map.entrySet()) {
            System.out.println("key: " + entry.getKey() + " value: " + entry.getValue());
        }

4.通过Map.values()遍历value,无法遍历key

for (String value : map.values()) {
            System.out.println(" value: " + value);
        }

5.通过Map.keySet()key,无法遍历value

for (String key : map.keySet()) {
            System.out.println(" key: " + key);
        }

完整代码

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * Map集合遍历的五种方式
 */
public class MapIterator {

    public static void main(String[] args) {
        Map map = new HashMap();
        map.put("a", "123");
        map.put("b", "245");
        map.put("c", "456");
        map.put("d", "789");

        System.out.println("第一种：通过Map.KeySet遍历key和value");
        System.out.println("------------------------------------");
        for (String key : map.keySet()) {
            String value = map.get(key);
            System.out.println("key: " + key + " value: " + value);
        }
        System.out.println("------------------------------------");

        System.out.println("第二种：通过Map.entrySet使用iterator遍历key和value");
        System.out.println("------------------------------------");
        Iterator.Entry> iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = iterator.next();
            System.out.println("key: " + entry.getKey() + " value: " + entry.getValue());
        }
        System.out.println("------------------------------------");

        System.out.println("第三种：通过Map.entrySet遍历key和value");
        System.out.println("------------------------------------");
        for (Map.Entry entry : map.entrySet()) {
            System.out.println("key: " + entry.getKey() + " value: " + entry.getValue());
        }
        System.out.println("------------------------------------");

        System.out.println("第四种：通过Map.values()遍历value,无法遍历key");
        System.out.println("------------------------------------");
        for (String value : map.values()) {
            System.out.println(" value: " + value);
        }
        System.out.println("------------------------------------");

        System.out.println("第五种：通过Map.keySet()key,无法遍历value");
        System.out.println("------------------------------------");

        for (String key : map.keySet()) {
            System.out.println(" key: " + key);
        }
        System.out.println("------------------------------------");

    }

}